This invention relates to apparatus and processes for cleaning photographic film, and more particularly to liquid cleaning systems for long lengths of photographic film, which systems neither significantly affect the image areas of the film nor cause significant detrimental liquid interaction with the film.
In the movie film and photographic industries, over the years, various techniques have been devised for cleaning film surfaces to eliminate dust, particulates and other materials which wear, abrade, or obstruct portions of the photographic image areas. Cleaning is regularly used before printing, but the methods typically used for cleaning have often affected the film itself. For example, one traditional method has been the use of mechanical cleaners, such as the "scrubber cleaner" in which rotary scrubber brushes remove the dirt, while a solvent such as 1-1-1 trichloroethane is employed to carry the dirt away from the film. Some mechanical cleaners can potentially scratch the film while solvents are being discontinued because of their introduction of pollutants into the atmosphere.
In a prior patent, U.S. Pat. No. 4,706,325, I disclose a film cleaner system using rotary brushes which has achieved substantial success in a number of film industry situations. This is a dry brushing system in which soft rotary brushes are disposed in pairs along and on opposite sides of the film path. Each brush of a pair spans a different part of the film width and is angled and rotated in such fashion that dust and other particulates, which tend to be concentrated along the film perforations, are impelled away from the center of the film toward the film edges. The brushes are displaced and angled so that they sweep across the opposite edge perforations and cover both sides of the film. Matter accumulating on each of the brushes is removed by contact with adjacent electrostatic discharge elements which are tube-shaped and slotted to serve additionally as suction devices. This system contacts the image areas of the film and minimizes scratching because soft brushes can be used. However, as stated at col. 5, lines 51-52 therein, "Brush speed is relatively low to avoid centrifugal force dislodging dirt from the brush." The limitations on use of this approach are more precisely viewed in terms of the difficulty of ensuring elimination of dirt particles under the complex forces which act on the particles, including mechanical adhesion, centrifugal force, electrostatic forces and vacuum forces. Taken together, they limit the throughput rate which can be achieved with this approach.
Another common existing method is the use of a cleaning solution, such as 1-1-1 trichloroethane which is excited with an ultrasonic transducer to dislodge dirt particles and transport them away from the film. With this ultrasonic cleaner, the film is easily dried because of the volatility of the trichloroethane. However, the use of solvent solutions is now being severely restricted, inasmuch as they present pollution and potential carcinogenic problems that are no longer acceptable. Using a non-volatile solution, such as water, has heretofore not been acceptable because photographic emulsions absorb water if exposed to water for any length of time. Consequently, the employment of the ultrasonic cleaner approach using water immersion would result in absorption of significant amounts of water that would have to be removed in a drying system called a "dry box." Because the standard in the industry involves cleaning at rates of 50 to 200 feet or more per minute, drying a water-saturated color negative at a speed of 100 feet per minute would entail many minutes of residence time and therefore would require a long path length. This in turn would involve several hundred rollers, large blowers, a heat exchanger, and a massive film transport mechanism, necessitating a dry box of several hundred cubic feet in volume. Moreover, the many rollers used in such a system inevitably introduce dirt into the just-cleaned film. For such reasons, feasible high speed cleaning approaches using water have not previously been devised for photographic film.